If there's one universal rule of computing, it's back up everything.

Not only can you erase a file by mistake, but the computer also isn't perfect. Chips can go bad. Even good chips will forget everything if the power is cut. Disk drives can fail unexpectedly and lose information permanently.

So you should always keep copies of your valuable data: your word-processing documents, your spreadsheets, your data-base files. And multiple levels of backup, from frequently saving your work in progress to occasionally making backup disks to store away from the computer, give you real security.

You also need to back up your programs. Now that most software isn't copy-protected, that's entirely possible. Although you can get replacement copies from most software companies, you may find yourself needing a replacement during that vital weekend work sprint as you strain to finish the big project. Even if the original program fails during a standard workday, it may take days or weeks to get the replacement. If the program is crucial, you're up a computer creek without a software paddle for all that time.

Backing up floppies isn't too hard, especially if you have two floppy drives. You just slide the original disk into one drive and the backup floppy into the other and use the DOS Copy or Diskcopy commands.

Backing up a hard disk isn't such a slight task. A 40-megabyte hard disk can be copied to a series of floppy disks. But even with a high-density floppy drive, you might need 20 to 30 floppy disks for the task. A low-density floppy could take 100 or more. And you can't just use the Diskcopy command to get all the files from all the directories and subdirectories.

Who wants to spend an hour pushing floppies into a drive and waiting for them to fill up? Folks with a lot of money can just buy a second hard disk and dedicate it to backup work. That's fast, but still takes some special batch file commands or knowledge of DOS tricks to make sure all the directories and subdirectories are copied from one disk to the other. Other people use tape backup systems, which can back up the information on a hard disk in 10 to 20 minutes. But there, too, you need software that can perform the backup, keeping track that all files are copied correctly.

But if you're like me, you don't change many files each day. You might create a few new word-processing documents and a spreadsheet or two, make small editing changes to a few more and add some information to a data base. If that's all you change, why should you have to copy again all those other program files and untouched data files?

With the right backup software, you don't have to.

In this subset of the utility programs field, the Norton Backup ($149, Peter Norton Computing, 1-213-319-2000) is getting a lot of press lately.

Peter Norton is famous for his books about the IBM PC and for his company's Norton Utilities program that helps recover accidentally erased files. Now the company, which recently became part of Symantec Corp., a Cupertino, Calif., software firm, has joined the ranks of companies providing backup software as well.

The Norton Backup lets you choose just how you want to back up your files, then it handles the job for you. It's very easy to install, automatically inspecting your PC to see what sort of memory and disk drives it has. And it comes with a clear, step-by-step manual that explains the commands and menus.

There are levels in the Norton Backup for beginners and more expert users. The beginner level lets you choose which files to back up and where to copy them. You see a graphic map of the directories and files on screen and can choose them individually or in groups, by type, name or other attributes.

Then the utility can move quickly to put those selected files onto the backup disk and can compress them in several ways so that the backup is even faster or so that the files take up less space on the backup disks. Future versions are supposed to support tape drives -- it's a bit odd that this first version doesn't offer that support.

You can choose complete backups or incremental backups -- where only the files that have changed since your last backup operation are copied. The utility keeps track of which files have changed, so you don't have to. There's on-line help at all times to explain how to use the commands.

When you need to "restore" files from the backup disks to your main hard disk, the commands work in pretty much the same way.

When you're restoring or backing up, the screen shows you just how many files are selected, how large they are, how much time it should take to move them, how much time has passed in the current operation and a bar graph showing progress.

On the advanced level, the Norton Backup offers more control over the process, plus the ability to save backup operations as "presets" that beginners then can run automatically. There's also a macro feature built in so any sequence of commands can be saved and replayed. You can save up to 50 presets, which can be handy when you work with a variety of data types or have network data to back up: The program supports networks and can back up from or to several disk drives in a single operation.

The Norton Backup is very fast. The menus seem clear at first glance but did have me stabbing at keys a few times, trying to figure out whether to push the space bar or the tab key -- but overall it is pretty easy to use. I think beginners will find it a bit intimidating, while experts will love the various preset and compression options -- though experts may be hungry for tape-drive support.

But the program's price is too high, considering that for a similar price you can buy a package such as PC Tools that contains a disk backup program along with a DOS "shell," disk caching and a dozen other utilities. The PC Tools backup program even offers timed backups -- in case you want to back up to a tape drive late at night -- something I didn't find in the Norton Backup.

If I didn't know about PC Tools or if the price were cut by 50 percent, I might be swayed by this slick backup utility. For now, though, I would rather buy another package that does most of the same things but offers lots more on other fronts.

Phillip Robinson is an author of books and articles about computers and an editor for Virtual Information of Sausalito, Calif.